---
title: 'Tutorial'
slug: /tutorial
---

## Introduction

In this hands-on tutorial, we will take a look at how we can use Yew to build web applications.
**Yew** is a modern [Rust](https://www.rust-lang.org/) framework for building front-end web apps using [WebAssembly](https://webassembly.org/).
Yew encourages a reusable, maintainable, and well-structured architecture by leveraging Rust's powerful type system.
A large ecosystem of community-created libraries, known in Rust as [crates](https://doc.rust-lang.org/book/ch07-01-packages-and-crates.html),
provide components for commonly-used patterns such as state management.
[Cargo](https://doc.rust-lang.org/cargo/), the package manager for Rust, allows us to take advantage of the
numerous crates available on [crates.io](https://crates.io), such as Yew.

### What we are going to build

Rustconf is an intergalactic gathering of the Rust community that happens annually.
Rustconf 2020 had a plethora of talks that provided a good amount of information.
In this hands-on tutorial, we will be building a web application to help fellow Rustaceans
get an overview of the talks and watch them all from one page.

## Setting up

### Prerequisites

To get started, let's make sure we have an up-to-date development environment.
We will need the following tools:

- [Rust](https://www.rust-lang.org/)
- [`trunk`](https://trunkrs.dev/)
- `wasm32-unknown-unknown` target, the WASM compiler and build target for Rust.

This tutorial also assumes you're already familiar with Rust. If you're new to Rust,
the free [Rust Book](https://doc.rust-lang.org/book/ch00-00-introduction.html) offers a great starting point for
beginners and continues to be an excellent resource even for experienced Rust developers.

Ensure the latest version of Rust is installed by running `rustup update` or by
[installing rust](https://www.rust-lang.org/tools/install) if you haven't already done so already.

After installing Rust, you can use Cargo to install `trunk` by running:

```bash
cargo install trunk
```

We will also need to add the WASM build target by running:

```bash
rustup target add wasm32-unknown-unknown
```

### Setting up the project

First, create a new cargo project:

```bash
cargo new yew-app
cd yew-app
```

To verify the Rust environment is set up properly, run the initial project using the cargo build tool.
After output about the build process, you should see the expected "Hello, world!" message.

```bash
cargo run
```

## Our first static page

To convert this simple command line application to a basic Yew web application, a few changes are needed.
Update the files as follows:

```toml title="Cargo.toml" {7}
[package]
name = "yew-app"
version = "0.1.0"
edition = "2021"

[dependencies]
+ yew = "0.19"
```

```rust ,no_run title="src/main.rs"
use yew::prelude::*;

#[function_component(App)]
fn app() -> Html {
    html! {
        <h1>{ "Hello World" }</h1>
    }
}

fn main() {
    yew::start_app::<App>();
}
```

Now, let's create an `index.html` at the root of the project.

```html title="index.html"
<!doctype html>
<html lang="en">
    <head> </head>
    <body></body>
</html>
```

### Start the development server

Run the following command to build and serve the application locally.

```bash
trunk serve --open
```

Trunk will open your application in your default browser, watch the project directory and helpfully rebuild your
application if you modify any source files. If you are curious, you can run `trunk help` and `trunk help <subcommand>`
for more details on what's happening.

### Congratulations

You have now successfully set up your Yew development environment and built your first Yew web application.

## Building HTML

Yew makes use of Rust's procedural macros and provides us with a syntax similar to JSX (an extension to JavaScript
which allows you to write HTML-like code inside of JavaScript) to create the markup.

### Converting classic HTML

Since we already have a pretty good idea of what our website will look like, we can simply translate our mental draft
into a representation compatible with `html!`. If you're comfortable writing simple HTML, you should have no problem
writing marking inside `html!`. It is important to note that the macro does differ from HTML in a few ways:

1. Expressions must be wrapped in curly braces (`{ }`)
2. There must only be one root node. If you want to have multiple elements without wrapping them in a container,
   an empty tag/fragment (`<> ... </>`) is used
3. Elements must be closed properly.

We want to build a layout that looks something like this in raw HTML:

```html
<h1>RustConf Explorer</h1>
<div>
    <h3>Videos to watch</h3>
    <p>John Doe: Building and breaking things</p>
    <p>Jane Smith: The development process</p>
    <p>Matt Miller: The Web 7.0</p>
    <p>Tom Jerry: Mouseless development</p>
</div>
<div>
    <h3>John Doe: Building and breaking things</h3>
    <img
        src="https://placehold.co/640x360.png?text=Video+Player+Placeholder"
        alt="video thumbnail"
    />
</div>
```

Now, let's convert this HTML into `html!`. Type (or copy/paste) the following snippet into the body of `app` function
such that the value of `html!` is returned by the function

```rust ,ignore
html! {
    <>
        <h1>{ "RustConf Explorer" }</h1>
        <div>
            <h3>{"Videos to watch"}</h3>
            <p>{ "John Doe: Building and breaking things" }</p>
            <p>{ "Jane Smith: The development process" }</p>
            <p>{ "Matt Miller: The Web 7.0" }</p>
            <p>{ "Tom Jerry: Mouseless development" }</p>
        </div>
        <div>
            <h3>{ "John Doe: Building and breaking things" }</h3>
            <img src="https://placehold.co/640x360.png?text=Video+Player+Placeholder" alt="video thumbnail" />
        </div>
    </>
}
```

Refresh the browser page, and you should see the following output displayed:

![Running WASM application screenshot](/img/tutorial_application_screenshot.png)

### Using Rust language constructs in the markup

A big advantage of writing markup in Rust is that we get all the coolness of Rust in our markup.
Now, instead of hardcoding the list of videos in the html, let's actually define them as a `Vec` of Rust objects.
We'll create a simple `struct` (in `main.rs` or any file of our choice) which will hold our data.

```rust
struct Video {
    id: usize,
    title: String,
    speaker: String,
    url: String,
}
```

Next, we will create instances of this struct in our `app` function and use those instead of hardcoding the data:

```rust
use website_test::tutorial::Video; // replace with your own path

let videos = vec![
    Video {
        id: 1,
        title: "Building and breaking things".to_string(),
        speaker: "John Doe".to_string(),
        url: "https://youtu.be/PsaFVLr8t4E".to_string(),
    },
    Video {
        id: 2,
        title: "The development process".to_string(),
        speaker: "Jane Smith".to_string(),
        url: "https://youtu.be/PsaFVLr8t4E".to_string(),
    },
    Video {
        id: 3,
        title: "The Web 7.0".to_string(),
        speaker: "Matt Miller".to_string(),
        url: "https://youtu.be/PsaFVLr8t4E".to_string(),
    },
    Video {
        id: 4,
        title: "Mouseless development".to_string(),
        speaker: "Tom Jerry".to_string(),
        url: "https://youtu.be/PsaFVLr8t4E".to_string(),
    },
];
```

In order to display them, we need to convert these `Vec`s into `Html`. We can do that by creating an iterator,
mapping it to `html!` and collecting it as `Html`:

```rust ,ignore
let videos = videos.iter().map(|video| html! {
    <p>{format!("{}: {}", video.speaker, video.title)}</p>
}).collect::<Html>();
```

And finally we need to replace the hardcoded list of videos with the `Html` we created from data:

```rust ,ignore {6-10}
html! {
    <>
        <h1>{ "RustConf Explorer" }</h1>
        <div>
            <h3>{ "Videos to watch" }</h3>
-           <p>{ "John Doe: Building and breaking things" }</p>
-           <p>{ "Jane Smith: The development process" }</p>
-           <p>{ "Matt Miller: The Web 7.0" }</p>
-           <p>{ "Tom Jerry: Mouseless development" }</p>
+           { videos }
        </div>
        // ...
    </>
}
```

## Components

Components are the building blocks of Yew applications. By combining components, which can be made of other components,
we build our application. By structuring our components for re-usability and keeping them generic, we will be able to use
them in multiple parts of our application without having to duplicate code or logic.

In fact, the `app` function we have been using so far is a component, called `App`. It is a "function component".
There are two different types of components in Yew.

1. Struct Components
2. Function Components

In this tutorial, we will be using function components.

Now, let's split up our `App` component into smaller components. We'll begin by extracting the videos list into
its own component.

```rust ,compile_fail
use yew::prelude::*;

struct Video {
    id: usize,
    title: String,
    speaker: String,
    url: String,
}

#[derive(Clone, Properties, PartialEq)]
struct VideosListProps {
    videos: Vec<Video>,
}

#[function_component(VideosList)]
fn videos_list(VideosListProps { videos }: &VideosListProps) -> Html {
    videos.iter().map(|video| html! {
        <p>{format!("{}: {}", video.speaker, video.title)}</p>
    }).collect()
}
```

Notice the parameters of our `VideosList` function component. A function component takes only one argument which
defines its "props" (short for "properties"). Props are used to pass data down from a parent component to a child component.
In this case, `VideosListProps` is a struct which defines the props.

:::important
The struct used for props must implement `Properties` by deriving it.
:::

In order for the above code to compile, we need to modify the `Video` struct like:

```rust {1}
#[derive(Clone, PartialEq)]
struct Video {
    id: usize,
    title: String,
    speaker: String,
    url: String,
}
```

Now, we can update our `App` component to make use of `VideosList` component.

```rust ,ignore {4-7,13-14}
#[function_component(App)]
fn app() -> Html {
    // ...
-    let videos = videos.iter().map(|video| html! {
-        <p>{format!("{}: {}", video.speaker, video.title)}</p>
-    }).collect::<Html>();
-
    html! {
        <>
            <h1>{ "RustConf Explorer" }</h1>
            <div>
                <h3>{"Videos to watch"}</h3>
-               { videos }
+               <VideosList videos={videos} />
            </div>
            // ...
        </>
    }
}
```

By looking at the browser window, we can verify that the lists are rendered as they should be.
We have moved the rendering logic of lists to its own component. This shortens the `App` component’s source code,
making it easier for us to read and understand.

### Making it interactive

The final goal here is to display the selected video. In order to do that, `VideosList` component needs to "notify" its
parent when a video is selected, which is done via a `Callback`. This concept is called "passing handlers".
We modify its props to take an `on_click` callback:

```rust ,ignore {4}
#[derive(Clone, Properties, PartialEq)]
struct VideosListProps {
    videos: Vec<Video>,
+    on_click: Callback<Video>
}
```

Then we modify the `VideosList` component to pass the "emit" the selected video to the callback.

```rust ,ignore {2-4,6-12,15-16}
#[function_component(VideosList)]
-fn videos_list(VideosListProps { videos }: &VideosListProps) -> Html {
+fn videos_list(VideosListProps { videos, on_click }: &VideosListProps) -> Html {
+    let on_click = on_click.clone();
    videos.iter().map(|video| {
+        let on_video_select = {
+            let on_click = on_click.clone();
+            let video = video.clone();
+            Callback::from(move |_| {
+                on_click.emit(video.clone())
+            })
+        };

        html! {
-            <p>{format!("{}: {}", video.speaker, video.title)}</p>
+            <p onclick={on_video_select}>{format!("{}: {}", video.speaker, video.title)}</p>
        }
    }).collect()
}
```

Next, we need to modify the usage of `VideosList` to pass that callback. But before doing that, we should create
a new component, `VideoDetails`, component that is displayed when a video is clicked.

```rust
use website_test::tutorial::Video;
use yew::prelude::*;

#[derive(Clone, Properties, PartialEq)]
struct VideosDetailsProps {
    video: Video,
}

#[function_component(VideoDetails)]
fn video_details(VideosDetailsProps { video }: &VideosDetailsProps) -> Html {
    html! {
        <div>
            <h3>{ video.title.clone() }</h3>
            <img src="https://placehold.co/640x360.png?text=Video+Player+Placeholder" alt="video thumbnail" />
        </div>
    }
}
```

Now, modify the `App` component to display `VideoDetails` component whenever a video is selected.

```rust ,ignore {4,6-11,13-15,24-29}
#[function_component(App)]
fn app() -> Html {
    // ...
+    let selected_video = use_state(|| None);

+    let on_video_select = {
+        let selected_video = selected_video.clone();
+        Callback::from(move |video: Video| {
+            selected_video.set(Some(video))
+        })
+    };

+    let details = selected_video.as_ref().map(|video| html! {
+        <VideoDetails video={video.clone()} />
+    });

    html! {
        <>
            <h1>{ "RustConf Explorer" }</h1>
            <div>
                <h3>{"Videos to watch"}</h3>
-               <VideosList videos={videos} />
+               <VideosList videos={videos} on_click={on_video_select.clone()} />
            </div>
+            { for details }
-            <div>
-                <h3>{ "John Doe: Building and breaking things" }</h3>
-                <img src="https://placehold.co/640x360.png?text=Video+Player+Placeholder" alt="video thumbnail" />
-            </div>
-        </>
    }
}
```

Don't worry about the `use_state` right now, we will come back to that later.
Note the trick we pulled with `{ for details }`. `Option<_>` implements `Iterator` so we can use it to display the only
element returned by the `Iterator` with the `{ for ... }` syntax.

### Handling state

Remember the `use_state` used earlier? That is a special function, called a "hook". Hooks are used to "hook" into
the lifecycle of a function component and perform actions. You can learn more about this hook, and others
[here](concepts/function-components/pre-defined-hooks#use_state).

:::note
Struct components act differently. See [the documentation](concepts/components/introduction) to learn about those.
:::

## Fetching data (using external REST API)

In a real world application, data will usually come from an API instead of being hardcoded. Let's fetch our
videos list from external source. For this we will need to add the following crates:

- [`gloo-net`](https://crates.io/crates/gloo-net)
  For making the fetch call.
- [`serde`](https://serde.rs) with derive features
  For de-serializing the JSON response
- [`wasm-bindgen-futures`](https://crates.io/crates/wasm-bindgen-futures)
  For executing Rust Future as a Promise

Let's update the dependencies in `Cargo.toml` file:

```toml title="Cargo.toml"
[dependencies]
gloo-net = "0.2"
serde = { version = "1.0", features = ["derive"] }
wasm-bindgen-futures = "0.4"
```

Update the `Video` struct to derive the `Deserialize` trait:

```rust ,ignore {1,3-4}
+ use serde::Deserialize;

- #[derive(Clone, PartialEq)]
+ #[derive(Clone, PartialEq, Deserialize)]
struct Video {
    id: usize,
    title: String,
    speaker: String,
    url: String,
}
```

Now as the last step, we need to update our `App` component to make the fetch request instead of using hardcoded data

```rust ,ignore {1,5-25,34-35}
+ use gloo_net::http::Request;

#[function_component(App)]
fn app() -> Html {
-    let videos = vec![
-        // ...
-    ]
+    let videos = use_state(|| vec![]);
+    {
+        let videos = videos.clone();
+        use_effect_with_deps(move |_| {
+            let videos = videos.clone();
+            wasm_bindgen_futures::spawn_local(async move {
+                let fetched_videos: Vec<Video> = Request::get("https://yew.rs/tutorial/data.json")
+                    .send()
+                    .await
+                    .unwrap()
+                    .json()
+                    .await
+                    .unwrap();
+                videos.set(fetched_videos);
+            });
+            || ()
+        }, ());
+    }

    // ...

    html! {
        <>
            <h1>{ "RustConf Explorer" }</h1>
            <div>
                <h3>{"Videos to watch"}</h3>
-                <VideosList videos={videos} on_click={on_video_select.clone()} />
+                <VideosList videos={(*videos).clone()} on_click={on_video_select.clone()} />
            </div>
            { for details }
        </>
    }
}
```

:::note
We're using `unwrap`s here because this is a demo application. In a real world app, you would likely want to have
[proper error handling](https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html).
:::

Now look at the browser to see everything working as expected... which would've been the case if it weren't for CORS.
In order to fix that, we need a proxy server. Luckily trunk provides that.

Update the following line:

```rust ,ignore {2-3}
// ...
-                let fetched_videos: Vec<Video> = Request::get("https://yew.rs/tutorial/data.json")
+                let fetched_videos: Vec<Video> = Request::get("/tutorial/data.json")
// ...
```

Now, rerun the server with the following command:

```bash
trunk serve --proxy-backend=https://yew.rs/tutorial
```

Refresh the tab and everything should work as expected.

## Wrapping up

Congratulations! You’ve created a web application that fetches data from an external API and displays a list of videos.

## What's next

Obviously, this application is very far from perfect or useful. After going through this tutorial,
you can use it as a jumping-off point to explore more advanced topics.

### Styles

Our apps look very ugly. There's no CSS, or any kind of styles.
Unfortunately, Yew doesn't offer a built-in way to style components. See [Trunk's assets](https://trunkrs.dev/assets/)
to learn how to add style sheets.

### More libraries

Our app made use of only a few external dependencies. There are lots of crates out there that can be used.
See [external libraries](more/external-libs) for more details.

### Learning more about Yew

Read our [official documentation](/docs/getting-started/introduction). It explains a lot of concepts in much more details.
To learn more about our the Yew API, see our [API docs](https://docs.rs/yew).
